Exposure classes BS EN 206-1

Concrete –
Complementary
British Standard to
BS EN 206-1 –
Part 1: Method of specifying and guidance for the specifier

 

Table A.1 Exposure classes 노출등급

Class designation	Class description	Informative examples applicable in the United Kingdom
No risk of corrosion or attack (X0 class)
X0	For concrete without reinforcement or embedded metal: all exposures except where there is freeze-thaw, abrasion or chemical attack For concrete with reinforcement or embedded metal: very dry	Unreinforced concrete surfaces inside structures Unreinforced concrete completely buried in soil classed as AC-1 and with a hydraulic gradient not greater than 5 Unreinforced concrete permanently submerged in non-aggressive water Unreinforced concrete surfaces in cyclic wet and dry conditions not subject to abrasion, freezing or chemical attack Reinforced concrete surfaces exposed to very dry conditions
Corrosion induced by carbonation (XC classes) A) (where concrete containing reinforcement or other embedded metal is exposed to air and moisture)
XC1	Dry or permanently wet	Reinforced and prestressed concrete surfaces inside enclosed structures except areas of structures with high humidity Reinforced and prestressed concrete surfaces permanently submerged in non-aggressive water
XC2	Wet, rarely dry	Reinforced and prestressed concrete completely buried in soil classed as AC-1 and with a hydraulic gradient not greater than 5B)
XC3 and XC4	Moderate humidity or cyclic wet and dry	External reinforced and prestressed concrete surfaces sheltered from, or exposed to, direct rain Reinforced and prestressed concrete surfaces subject to high humidity (e.g. poorly ventilated bathrooms, kitchens) Reinforced and prestressed concrete surfaces exposed to alternate wetting and drying Interior concrete surfaces of pedestrian subways not subject to de-icing salts, voided superstructures or cellular abutments Reinforced or prestressed concrete beneath waterproofing
Corrosion induced by chlorides other than from sea water (XD classes) A) (where concrete containing reinforcement or other embedded metal is subject to contact with water containing chlorides, including de-icing salts, from sources other than from sea water)
XD1	Moderate humidity	Concrete surfaces exposed to airborne chlorides Reinforced and prestressed concrete wall and structure supports more than 10 m horizontally from a carriageway Bridge deck soffits more than 5 m vertically above the carriageway Parts of structures exposed to occasional or slight chloride conditions
XD2	Wet, rarely dry	Reinforced and prestressed concrete surfaces totally immersed in water containing chlorides C) Buried highway structures more than 1 m below adjacent carriageway
XD3	Cyclic wet and dry	Reinforced and prestressed concrete walls and structure supports within 10 m of a carriageway Bridge parapet edge beams Buried highway structures less than 1 m below carriageway level Reinforced pavements and car park slabs
Corrosion induced by chlorides from sea water (XS classes) A), D) (where concrete containing reinforcement or other embedded metal is subject to contact with chlorides from sea water or air carrying salt originating from sea water)
XS1	Exposed to airborne salt but not in direct contact with sea water	External reinforced and prestressed concrete surfaces in coastal areas
XS2	Permanently submerged	Reinforced and prestressed concrete surfaces completely submerged and remaining saturated, e.g. concrete below mid-tide level C)
XS3	Tidal, splash and spray zones	Reinforced and prestressed concrete surfaces in the upper tidal zones and the splash and spray zones E)
Freeze-thaw attack (XF classes) (where concrete is exposed to significant attack from freeze-thaw cycles whilst wet)
XF1	Moderate water saturation without de-icing agent	Vertical concrete surfaces such as façades and columns exposed to rain and freezing Non-vertical concrete surfaces not highly saturated, but exposed to freezing and to rain or water
XF2	Moderate water saturation with de-icing agent	Concrete surfaces such as parts of bridges, which would otherwise be classified as XF1, but which are exposed to de-icing salts either directly or as spray or run-off
XF3	High water saturation without de-icing agent	Horizontal concrete surfaces, such as parts of buildings, where water accumulates and which are exposed to freezing Concrete surfaces subjected to frequent splashing with water and exposed to freezing
XF4	High water saturation with de-icing agent or sea water F)	Horizontal concrete surfaces, such as roads and pavements, exposed to freezing and to de-icing salts either directly or as spray or run-off Concrete surfaces subjected to frequent splashing with water containing de-icing agents and exposed to freezing
Chemical attack (XA classes) (where concrete is exposed to chemical attack) Use Table A.2 to determine the ACEC-class. See BRE Special Digest 1 [1] for guidance on site investigation
A) The moisture condition relates to that in the concrete cover to reinforcement or other embedded metal but, in many cases, conditions in the concrete cover can be taken as being that of the surrounding environment. This might not be the case if there is a barrier between the concrete and its environment (see A.3). B) For concrete in soil classed as AC-2 or above or an element with a hydraulic gradient greater than 5, the ACEC class is used to determine the concrete quality and minimum cover to reinforcement (see A.4.4). C) Reinforced and prestressed concrete elements where one surface is immersed in water containing chlorides and another is exposed to air are potentially a more severe condition, especially where the dry side is at a high ambient temperature. Specialist advice should be sought where appropriate, to develop a specification that is appropriate to the actual conditions likely to be encountered. D) The rate of ingress of chloride into the concrete will depend on the concentration at its surface: brackish groundwater (chloride content less than 18 g/l) will be less severe than exposure to sea water. E) Exposure XS3 covers a range of conditions. The most extreme conditions are in the spray zone. The least extreme is in the  tidal zone where conditions can be similar to those in XS2. The recommendations given in this annex take into account the most extreme conditions within this class. F) It is not normally necessary to classify in the XF4 exposure class those parts of structures located in the United Kingdom which are in frequent contact with the sea.